Drain plugs find use in a wide variety of applications. Household use in a sink or tub is well known, but drain plugs are also needed in industrial and marine applications. Small boats have drain openings below the water line and generally at the stern of the boat to allow drainage of water from inside the boat when the boat has been taken from the water for storage or maintenance. Depending on the design of the boat and the accessibility of the opening, it is frequently necessary to insert the drain plug from the outside of the boat. Some boats have wells inside the boat for fishermen to keep the live fish which they have caught and these live wells often have a drain opening with a drain plug inserted from within the boat. The use of drain plugs in boats introduce several unique problems. Traditional plugs are made in brass and aluminum which may be used in wooden, fiberglass or non-metallic boats. However, with aluminum boats, a dissimilar metal such as brass will cause corrosion of the boat. Furthermore, the traditional plugs, if loosened in the drain opening can easily be lost if fitted from the outside of the boat. In the live well it is difficult to locate the plug if in the bottom of dirty water. In either event, it is urgent that the plug be reinserted in the opening before water fills the boat and the boat sinks.
U.S. Pat. No. 2,199,964 discloses a stopper, intended primarily for household use, which has an outer body and an inner metallic cup-shaped expander which can be raised and lowered within the body by movement of a lever or a finger piece. U.S. Pat. No. 4,103,372 teaches a pop-up drain plug which is closed by pressing on a cover member to move a latch pin over a camming surface which activates a ball and spring. Release of the drain plug is also produced by pressure on the cover member. Despite these teachings, a need exists for an easily used drain plug which is non-metallic so as to avoid corrosion effects and which will float for rapid retrieval. In addition, the drain plug must be easily and inexpensively manufactured.